Method for treating organohalogen compounds with catalyst

ABSTRACT

A treating method for decomposing organohalogen compounds such as chlorofluorocarbons (CFC), trichloroethylene, methyl bromide, halon, and the like, effectively, with a high activity of catalyst is provided. 
     Organohalogen compounds are decomposed by contacting at a temperature in a range of 200°˜500° C. with catalyst which comprises titania and tungsten oxide by an atomic ratio of Ti and W in a range from 20 mol % to 95 mol % Ti and from 5 mol % to 80 mol % W, and at least surface of the titania is covered with porous layer of tungsten oxide. 
     In accordance with the present invention, organic compounds containing any of fluorine, chlorine, and bromine can be decomposed with a high efficiency, and the activity of the catalyst can be maintained for a long time.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a treating method for decomposinghalogenated organic compounds such as chlorofluorocarbons (CFC group,for instance flon), trichloroethylene, methyl bromide, and halon bymaking the compounds contact with catalyst effectively. Further, thepresent invention relates to the catalyst used in the treating methodfor decomposing organohalogen compounds, a preparing method thereof, andtreating apparatus for the decomposition.

2. Description of the Prior Art

Organohalogen compounds containing fluorine, chlorine, or bromine suchas chlorofluorocarbons, trichloroethylene, methyl bromide, halon, andthe like are widely used as foaming agents, refrigerants, fireextinguisher, fumigants, and the like. However, the above describedorganohalogen compounds cause destruction of the ozone layer, and haveserious influences such as generation of carcinogens and the like to theenvironment.

Therefore, various treating methods for recovering and decomposing theorganohalogen compounds have been investigated. As treating methods fordecomposing organohalogen compounds, a method using catalyst, a methodusing combustion at high temperature such as 800°˜900° C., a methodusing plasma, and others are well known. Among them, the methods usingcombustion and plasma consume a large amount of fuel, and electricpower, and have low energy efficiencies. Further, these methods have aproblem such that reactor walls are damaged by generated corrosivehalogens. Especially, the method using plasma has a large amount ofenergy loss because a high temperature exceeding 6000° C. is used. Onthe contrary, the method using catalyst is a superior method if thecatalyst has a high activity because only a small amount of energy isrequired.

As for the method using catalyst, a method using catalyst containingtitania was disclosed in JP-B-6-59388 (1994). A catalyst containingtitania and tungsten oxide, and a catalyst containing titania andvanadium oxide are described in the reference. However, organohalogencompounds to be contacted with the above disclosed catalysts arerestricted to the organohalogen compounds having only one carbon atomwith no carbon-hydrogen bond in a gas flow state, and embodiments in thereference showed only a case for treating carbontetrachloride of ppmorder. The catalyst containing titania and tungsten oxide is defined asTiO₂ containing tungsten oxide as W metal by a content of about 0.1˜20%by weight (if converted to atomic percentage, Ti within a range from 92mol % to 99. 96 mol %, W within a range from 0.04 mol % to 8 mol %).

As for catalytic poison of the organohalogen compounds, fluorinecompounds have larger influence than chlorine compounds. Accordingly, acatalyst which has a high activity to the organohalogen compoundscontaining not only chlorine, but also fluorine, bromine, and the like,is required. Further, the catalyst having a continuity in its activityis desired.

SUMMARY OF THE INVENTION OBJECTS OF THE INVENTION

One of the objects of the present invention is to provide a treatingmethod for decomposing organohalogen compounds by making the compoundscontact with catalyst having a high activity not only fororganochlorocompounds, but also for organofluorocompounds andorganobromocompounds, and a continuity of the activity.

Further, one of the objects of the present invention is to provide apreparing method for the above catalyst, and treating apparatus fordecomposing organohalogen compounds.

Methods for solving the problem

Feature of the catalyst relating to the present invention are in thatthe catalyst is composed of titania and tungsten oxide by Ti in a rangefrom 20 mol % to 95 mol %, W in a range from 80 mol % to 5 mol % inatomic ratio of Ti and W, and at least surface of the titania is coveredwith porous layers of tungsten oxide.

Titanium and tungsten can be contained in a state of a mixture ofoxides, or conjugated oxides. Tungsten oxides are contained mainly in aform of WO₃.

The present invention is based on a finding that, in order to have ahigh activity to all organohalogen compounds including any of halogenssuch as chlorine, fluorine, bromine, and the like, contained ratio oftitanium and tungsten is important, and that it is important to coversurface of the titanium with porous layers of tungsten oxide.

The catalyst composed of titania and tungsten oxide, which is disclosedin JP-B-6-59388 (1994), is not provided with porous layers of tungstenoxide at surface of the titania, and accordingly, the catalyst does nothave any high activity to organohalogen compounds containing fluorine,bromine, and the like other than chlorine.

The porous layer of tungsten oxide in the catalyst of the presentinvention can exist only at surface of TiO₂ particles, or at bothsurface and interior of the TiO₂ particles. Existence at both surfaceand interior of the TiO₂ particles is rather preferable. Thickness ofthe porous layer composed of tungsten oxide is preferably in a range of1 Å˜5 mm. If the thickness of the porous layer of tungsten oxide is toothin, TiO₂ is readily influenced with catalytic poison of halogens. Ifthe thickness of the porous layer is too thick, the activity of thecatalyst decreases.

The catalyst of the present invention can contain at least one ofelement selected from a group of sulfur, phosphorus, molybdenum, andvanadium. By adding the above element, durability of the catalyst can beimproved. The above elements are preferably contained into the catalystin a range of 0.001˜30 mol % in total to titanium atoms. Sulfur assulfates, phosphorus as phosphates, and molybdenum and vanadium asoxides are contained.

If the organohalogen compound is a molecule having a carbon atom, theatomic ratio of Ti and W is preferably in a range from 40 mol % to 90mol % for Ti and a range from 10 mol % to 60 mol % for W. If theorganohalogen compound is a molecule having two carbon atoms, becausethe number of halogen elements contained in the molecule increases, theatomic ratio of Ti and W is preferably in a range from 20 mol % to 85mol % for Ti and a range from 15 mol % to 80 mol % for W in order toincrease thickness of the porous layer made of WO₃ covering surface ofthe TiO₂ particle.

The catalyst of the present invention can be used by being formed invarious shapes such as beads, granules, pellets, and honeycombs. As forforming methods, extrusion, punch-pelletizing, roll-pelletizing, andothers can be used. In forming the catalyst, binders such as aluminacement, calcium-sodium cement, other ceramics, or organic compounds canbe added in order to increase mechanical strength of the catalyst, or toincrease specific surface of the catalyst.

The catalyst of the present invention can be used in a condition beingimpregnated into granular carrier such as alumina and silica byimpregnation and other methods. Further, the catalyst of the presentinvention or the granular carrier such as alumina and silica whichcarrying the catalyst of the present invention can be used in a coatedstate on ceramics, honeycomb or plate made of metal.

Gist of the treating method for decomposing organohalogen compounds ofthe present invention is in contacting gas flow containing organohalogencompounds with the above described catalyst at 200°˜500° C. underexistence of water vapor. In accordance with the above process, theorganohalogen compounds can be converted to carbon dioxide andhalogenated hydrogen, or carbon monoxide, carbon dioxide, andhalogenated hydrogen. When the organohalogen compound is CFC 113(1,1,2-trichloro-1,2,2-trifluorocarbon) the compound is decomposed tocarbon monoxide, carbon dioxide, and halogenated hydrogen. When theorganohalogen compound is CFC 11 and CFC 12, the compound is decomposedto carbon dioxide, and halogenated hydrogen. In accordance with thetreating method of the present invention, reactivity of the catalyst byhalogen contained in the decomposition products of the organohalogencompounds is little, and the catalyst maintains its activity for a longtime.

When contacting the gas flow containing the organohalogen compounds withthe catalyst, it is desirable to make the content of the organohalogencompounds in the gas flow 30% by volume or less. If the content of theorganohalogen compounds in the gas flow is higher than 30% by volume,the conversion rate of the organohalogen compounds decreases and apossibility that the organohalogen compounds releases without beingdecomposed becomes high. The lower limit of content of the organohalogencompounds in the gas flow is desirably at least 1000 ppm. If the contentof the organohalogen compounds is less than 1000 ppm, an energy lossbecomes problem although the energy necessary for decomposition of theorganohalogen compounds itself is small.

When treating the organohalogen compound containing one carbon atom,concentration of the organohalogen compound in the gas flow isespecially desirable in a range of 0.1˜30% by volume. When treating theorganohalogen compound containing two carbon atoms, concentration of theorganohalogen compound in the gas flow is especially desirable in arange of 0.1˜10% by volume. In order to adjust the concentration of theorganohalogen compound, addition of air, and the like, after recovery ofthe organohalogen compound is desirable.

The amount of water vapor is an effective amount necessary fordecomposing the organohalogen compound. For instance, when decomposingthe organohalogen compound containing two carbon atoms, existence ofwater vapor in the gas flow at least three times in mols to theorganohalogen compound is preferable.

As for preparing methods of the catalyst relating to the presentinvention, an impregnation method wherein a solution containing W isimpregnated into TiO₂ granules, and subsequently, the granules arecalcined to convert the W to WO₃, a method wherein a solution containingW is applied onto TiO₂ granules, or a vapor deposition method can beused.

When the impregnation method is used, individual fine TiO₂ granules iscoated with W ions, and uniformity is preferable. When a large amount oftungsten oxide is used, W ions are further coated onto surface ofcoagulated TiO₂ granules which are made by coagulating individual fineTiO₂ granules.

When preparing the catalyst by the impregnation method, the atomic ratioof Ti and W must be within a range of 20 mol %˜90 mol % for Ti and 10mol %˜80 mol % for W. In a case using the impregnation method, thesurface of the TiO₂ granules can not be covered entirely with the porouslayer of WO₃ if the atomic percentage of W to Ti does not exceed 10 mol%. If the surface of the TiO₂ granules can not be covered entirely withthe porous layer of WO₃, poisonous effect by halogen is generated atsurface exposed portion of the TiO₂ granules, for instance, TiOF₂ isgenerated at the surface exposed portion of the TiO₂ granules and theactivity of the catalyst decreases gradually.

When the catalyst is prepared by the vapor deposition method or theapplication method, the porous layer of WO₃ can be formed on the surfaceof the TiO₂ granules with a small amount of W such as 5 mol % in atomicratio.

In preparing the catalyst of the present invention, the catalyst ispreferably prepared by using TiO₂ granules which are obtained bygranulation. The granules obtained by granulation have inside cavitiesof uniform size and their porosity is readily controllable because thegranules are prepared by the steps of pulverizing raw material,fabricating by pressing, pulverizing again, and screening to selectgranules of a desired diameter. As for the granulation, theroll-pelletizing method is most preferable.

As the raw material of Ti for preparing the catalyst of the presentinvention, various compounds which generate titanium oxide by heatingcan be used in addition to titanium oxide.

One of the effective methods is such that hydroxide precipitation isgenerated by adding water, ammonia water, or alkaline water solution tothe titanium raw material such as titanates, titanium sulfate, titaniumchloride, and organotitanium compounds, and titania is finally preparedby calcining the precipitation.

As for the raw material of W, tungsten oxide, tungstic acid, andammonium paratungstate can be used. A raw material containing bothphosphorus and tungsten such as ammonium phosphotungstate can also beused.

The catalyst of the present invention maintains its activity longer asactive points in the catalyst is more acidic. Therefore, the catalystpreferably contains components to enhance acidity of the catalyst suchas S, P, and the like. The S exists in a form of oxide ion such as asulfate ion.

Even if the catalyst is composed of only TiO₂, the catalyst has highactivity for decomposing the organohalogen compounds. However, if theorganohalogen compounds is an organic compound containing fluorine, theactive sites form TiOF₂, the TiOF₂ releases from the catalyst, thenumber of the active points in the catalyst decreases, and accordingly,the activity of the catalyst decreases gradually. On the contrary,tungsten oxide hardly react with fluorine. Therefore, poisoning offluorine to TiO₂ can be prevented by coating the TiO₂ with porous layerscomposed of tungsten oxide. Further, new strongly acidic active pointswhich are hardly deteriorated by fluorine are generated at boundaries ofthe TiO₂ and the tungsten oxide WO₃.

Tungsten oxide WO₃ has smaller specific surface area than TiO₂, andaccordingly, it is not effective to prepare the catalyst only by thetungsten oxide.

The organohalogen compounds which are objects of the treatment of thepresent invention are organic compounds containing at least one offluorine, chlorine, and bromine, for instance, such as variouschlorofluorocarbon, trichloroethylene, methyl bromide, and the like.

Take CFC 113 and methyl bromide for examples, representative reactionformulas relating to the treating method for decomposing organohalogencompounds can be indicated as follows;

    C.sub.2 Cl.sub.3 F.sub.3 +3H.sub.2 O→CO+CO.sub.2 +3HCl+3HF

    CH.sub.3 Br+3/2O.sub.2 →CO+HVr+H.sub.2 O

As the above formulas reveal, when the organohalogen compound containingtwo carbon atoms is decomposed, it is necessary to exist water vapor atleast 3 mols to the organohalogen compound in the treated gas.

Reaction temperature, that is a temperature whereat the gas flowcontaining the organohalogen compound contacts with the catalyst, ispreferably in a range of 200°˜500° C. Therefore, heating the gas flowcontaining the organohalogen compounds, or heating a reactor whichcontains the catalyst is preferable. If the reaction temperature exceeds500° C., a reaction of the catalyst with fluorine starts, and theactivity of the catalyst decreases gradually. The reaction temperaturefor decomposing the organohalogen compounds containing one carbon atomis especially preferable in a range of 250°˜450° C. The reactiontemperature for decomposing the organohalogen compounds containing twocarbon atoms is especially preferable in a range of 300°˜500° C.

Reaction time for contacting the gas flow containing the organohalogencompounds is very short, for instance, one second is sufficient fordecomposing the organohalogen compounds. Accordingly, a space velocityper unit time is variable in a wide range such as 500˜100,000/hour. Thespace velocity for treating the organohalogen compound containing onecarbon atom is especially preferable in a range of 1,000˜50,000/hour,and the space velocity for treating the organohalogen compoundcontaining two carbon atoms is especially preferable in a range of500˜10,000/hour.

A reactor for performing the treating method of the present inventioncan be of an ordinary fixed bed type, a mobile bed type, or a fluidizedbed type. However, as corrosive gas such as HF, HCl, and the like aregenerated as decomposed gases in the process of the treating method, thereactor must be manufactured with corrosion resistant material againstthe above corrosive gases.

An apparatus for performing the treating method of the present inventionpreferably comprises, in addition to the above described reactor, meansfor adjusting concentration of the organohalogen compound in the gasflow, for instance, means for supplying air to the gas flow, means forheating at least one of the gas flow and the catalyst in order tocontact the gas flow containing the organohalogen compound with thecatalyst at a reaction temperature in a range of 200°˜500° C., means forsupplying an effective amount of water vapor for decomposing theorganohalogen compound to the gas flow, and an alkali washing vessel forwashing the gas flow passing through the catalytic layer to neutralize apart of carbon dioxide and halogenated hydrogen which are decompositionproducts of the organohalogen compound.

After the alkali washing vessel, means for adsorbing carbon monoxidewhich is a decomposition product of the organohalogen compound isfurther preferably provided.

When the organohalogen compound is in liquid state at the roomtemperature, the organohalogen compound is conducted to the catalyticlayer after heated to be gaseous state. As methods for heating theorganohalogen compound, an electric heater can be used. Further, theorganohalogen compound and water vapor can be mixed with burning gassuch as propane, kerosene, town gas, and the like, and is conducted tothe catalytic layer. As for the material of the reactor filled with thecatalyst, corrosive materials such inconel, hastelloy, and the like, arepreferable. As for the structure of the alkali washing vessel, a type ofthe vessel wherein alkali solution is sprayed for washing the gas ispreferable because clogging of pipes by deposition of crystals is hardlygenerated. A method wherein the decomposition produced gas is bubbledinto an alkaline solution, or a method wherein the decompositionproduced gas is washed in a packed tower can be used.

The treating apparatus for decomposition relating to the presentinvention can be portable by a truck or another vehicle. Places wherethe above apparatus to be carried into are such as junk yard for wastedrefrigerators, automobiles, and the others, and store houses forcylinders filled with the organohalogen compounds.

In accordance with the treating method of the present invention, thecatalyst is hardly deteriorated. Therefore, an exchange operation of thecatalyst is unnecessary or very scarce.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph indicating a relationship between conversion rate ofthe organohalogen compound and reaction time,

FIG. 2 is a graph indicating a relationship between conversion rate ofthe organohalogen compound and reaction time,

FIG. 3 is a graph indicating a relationship between conversion rate ofthe organohalogen compound and tungsten content,

FIG. 4 is a graph indicating a relationship between conversion rate ofthe organohalogen compound and thickness of WO₃ porous layer,

FIG. 5 is a graph indicating a relationship between conversion rate ofthe organohalogen compound and reaction time,

FIG. 6 is a graph indicating a relationship between conversion rate ofCFC 12 and CFC 12 concentration,

FIG. 7 is a graph indicating a relationship between conversion rate ofthe organohalogen compound and reaction time,

FIG. 8 is a graph indicating a relationship between conversion rate ofthe organohalogen compound and reaction time,

FIG. 9 is a graph indicating a relationship between conversion rate ofthe organohalogen compound and reaction time,

FIG. 10 is a graph indicating a relationship between conversion rate ofthe organohalogen compound and reaction time,

FIG. 11 is a graph indicating a relationship between conversion rate ofthe organohalogen compound and reaction time,

FIG. 12 is a schematic drawing indicating a composition of an apparatusfor decomposing organohalogen compound for performing the method of thepresent invention, and

FIG. 13 is a schematic drawing indicating another embodiment of theapparatus for decomposing organohalogen compound.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention are explained, but thescope of the present invention is not restricted by the embodiments.

(Embodiment 1)

In the present embodiment, dependence of catalytic activity on ratio ofTi to W, and various kinds of objective gases for treating is explainedon the catalyst prepared by the impregnation method.

(Experiment 1)

Catalytic activity was compared using the catalyst of the presentinvention having an atomic ratio of Ti and W of 8:2 (mol %) and acatalyst of a comparative example having an atomic ratio of Ti and W of9.5:0.5 (mol %) by decomposing treatment of an organohalogen compoundcomposed of CFC 12.

The catalyst of the present invention was prepared by the steps ofpulverizing granular titanium oxide (made by Sakai Chemical Co. CS-224)of 2˜3 mm in diameter, sieving the pulverized granules to be 0.5˜1 mm indiameter, drying at 120° C. for 2 hours, subsequently, impregnating thetitanium oxide granules into a hydrogen peroxide aqueous solutiondissolving ammonium paratungstate 82.2 gram per 100 grams of titaniumoxide, drying at 120° C. for 2 hours, and calcining at 500° C. for 2hours.

In order to examine cross sections of the catalyst, the catalyst wasmounted into a resin of which main component was epoxy resin. A whitelayer was observed at boundaries of the granular catalyst and the resinby SEM (scanning electron microscope) observation of the cross sectionof the catalyst. The white layer was confirmed as W component by anobservation with electron microprobe analyzer. Thickness of the whitelayer was about 10⁵ Å. As a result of analysis, it was revealed that thecatalyst had an atomic ratio of Ti and W of 8:2 (mol %), and contained Scomponent 6.9 mol % to Ti atoms. The S component was confirmed to be assulfate.

The preparing method of the catalyst of the comparative example was sameas the preparing method of the catalyst of the present invention exceptimpregnating the titanium oxide granules into a hydrogen peroxideaqueous solution dissolving ammonium paratungstate 17.3 grams instead of82.2 gram per 100 grams of titanium oxide. The catalyst of thecomparative example had an atomic ratio of Ti and W of 9.5:0.5 (mol %),and contained S component 6.9 mol % to Ti atoms. The S component wassulfate. The cross section of the catalyst of the comparative examplewas observed by scanning electron microscope. However, no white layerwas observed. Because the amount of tungsten oxide is small, tungstenoxide existed only inside of the titania granules and the tungsten oxidewas not observed at the surface of the titania granules.

The experiment of the decomposing treatment of the organohalogencompound CFC 12 was performed as follows;

A cylinder of 16 mm in diameter made of inconel was used as a reactor, acatalytic layer was arranged at middle of the reactor, and athermocouple protecting tube of 3 mm in outer diameter made of inconelwas inserted into inside of the reactor. The temperature of the catalystwas determined by the thermocouple during the decomposing treatment. Thereactor was heated by an electric furnace. Water vapor was adjusted bysupplying a designated amount of pure water to the upper part of thereactor by a pump to evaporate.

The composition of the objective treating gas was as follows;

    ______________________________________                                        CFC 12             3% by volume                                               water vapor       15% by volume                                               oxygen            10˜20% by volume                                      nitrogen          residual                                                    ______________________________________                                    

The objective treating gas having the above composition was supplied tothe reactor, decomposition produced gas passing through the catalyticlayer was bubbled into an alkali aqueous solution, and concentration ofCFC 12 in the gas passing through the alkali aqueous solution wasdetermined by FID (flame ionization detector) gas chromatography. Thespace velocity of the gas was 3,000/hour, and the temperature of thecatalyst in the reactor was 440° C. Conversion rate of the organohalogencompound was calculated by the following equation;

Conversion rate=1--(the amount of organohalogen compound at outlet/theamount of supplied organohalogen compound) X 100%

Variation of catalytic activity of the catalyst of the present inventionand the comparative example catalyst during a continuous 500 hours testis shown in FIG. 1. The abscissa of FIG. 1 indicates the reaction time,and the ordinate indicates conversion rate of the organohalogencompound. The activity of the catalyst of the present invention did notdecrease during the continuous 500 hours test, but the activity of thecatalyst of the comparative example decreased after 200 hours in thetest. Deposition of TiOF₂ was observed at the decomposition produced gasoutlet located at the lower portion of the reactor filled with thecomparative example catalyst.

(Experiment 2)

The activity of the catalyst of the present invention prepared in theabove experiment 1 was examined with changing the objective treating gasto CFC 113 which has two carbon atoms. The result of the examination isindicated in FIG. 2. The testing conditions were the same as theexperiment 1 except the reaction time. In this case, the reaction timewas continuous 100 hours. The catalyst of the present invention alsoindicated a high activity for decomposing treatment of CFC 113.

(Experiment 3)

The activity of the catalyst for decomposing treatment of CFC 12 wasexamined with changing the atomic ratio of Ti and W. The catalyst wasprepared by the same method as the experiment 1. Concentration of CFC 12was made higher as 6% by volume than that of the experiment 1. Othertesting conditions were the same as the experiment 1.

FIG. 3 indicates a relationship between conversion rate of CFC 12 andcontaining ratio of Ti and W. The conversion rate was determined at twohours after starting of the reaction. The catalyst of the presentinvention containing W in a range of 10˜80 mol % indicated a highconversion rate as at least 99%. In UNEP (United Nations EnvironmentProject), the conversion rate at least 99% is deemed as an authorizedtreating method for CFC, and the catalyst of the present inventionsatisfies the above condition.

Thickness of the porous layer composed of WO₃ varies depending on Wcontent. FIG. 4 indicates a relationship between the thickness of theWO₃ porous layer and the conversion rate of the organohalogen compound.The conversion rate were determined at two hours after starting of thereaction as same as FIG. 3.

(Experiment 4)

The activity of the catalyst of the present invention prepared in theabove experiment 1 was examined with changing the objective treating gasto CFC 11. In the composition of the objective treating gas,concentration of the CFC 11 was 3% by volume. The testing conditionswere the same as the experiment 1 except the reaction time. In thiscase, the reaction time was continuous 20 hours. The result of theexamination is indicated in FIG. 5. The conversion rate of CFC 11reached at 99.9%, and decrease of the activity of the catalyst was notobserved at all.

(Experiment 5)

The activity of the catalyst of the present invention prepared in theabove experiment 1 was examined with changing concentration of theobjective treating gas. The composition of the objective treating gaswas the same as that of the experiment 1 except varying theconcentration of CFC 12 in a range of 1˜10% by volume.

The result of the examination is indicated in FIG. 6. The conversionrate was determined at one hour after starting of the reaction. Atendency that the conversion rate of CFC 12 lowers as the concentrationof CFC 12 in the treating gas increases is observed. The catalyst of thepresent invention has a high conversion rate as at least 99% at thespace velocity of 3,000/hour under a condition that the concentration ofCFC 12 is in a range which does exceed 10% by volume.

(Experiment 6)

The activity of the catalyst of the present invention prepared in theabove experiment 1 was examined with changing reaction temperatures at440° C. and 600√ C. The experiment was performed with respective twokinds of CFC such as CFC 11 and CFC 12. The concentrations of the CFC 11and the CFC 12 were both 3% by volume. Other experimental conditionswere the same as the experiment 1.

The result of the examination is indicated in FIG. 7. The conversionrate was determined at one hour after starting of the reaction. When thereaction temperature was 440° C., no decrease of the activity wasobserved during continuous 100 hours test. However, when the reactiontemperature was 600° C., the activity of the catalyst decreased as thereaction time elapsed.

(Embodiment 2)

In the present embodiment, dependency of the activity of the catalyst onmaterials such as TiO₂ or W, and on preparing methods of the catalystwas examined. The decomposing treatment was performed on CFC 12. Themethod of the experiment and the composition of the objective treatinggas were the same as the experiment 1 except the reaction time. Thereaction time was continuous 10 hours.

(Experiment 7)

The activity of the catalyst was examined with changing size of the TiO₂granules. Concretely, the catalyst was prepared by the steps of dryingcommercially available granular TiO₂ (made by Sakai Chemical Co.,CS-300) having a diameter in a range of 0.5˜1 mm at 120° C. for twohours, and impregnating hydrogen peroxide aqueous solution dissolvingammonium paratungstate 82.2 g into the TiO₂ granules 100 g, drying againthe TiO₂ granules at 120° C. for 2 hours after the impregnation, andcalcining the TiO₂ granules at 500° C. for 2 hours. A relation betweenthe conversion rate of CFC 12 and the reaction time when the catalystprepared by the above described method was used is indicated in FIG. 8.The higher conversion rate was obtained with the catalyst having smalland uniform diameters as the catalyst in the experiment 1 than thepresent catalyst, but the difference of the conversion rate is small.

(Experiment 8)

The activity of the catalyst which was prepared using TiO₂ granulesmanufactured by granulation was examined.

As for raw material titania, granular titanium oxide (made by SakaiChemical Co., CS-224) of 2˜3 mm in diameter was pulverized in anautomatic mortar to be powder of 0.5 mm or less in diameter, the powderwas dried at 120° C. for 2 hours, and calcined at 500° C. for 2 hours.Then, the powder was loaded into a die and fabricated by pressing with apressure of 500 kgf/cm². The pressure for the fabrication is preferablyin a range of 250˜3000 kgf/cm².

The fabricated body was crashed and sieved to obtain titanium oxidegranules of 0.5˜1 mm in diameter. Then, a hydrogen peroxide aqueoussolution dissolving ammonium paratungstate 82.2 g was impregnated intothe obtained TiO₂ granules 100 g. After the impregnation, the TiO₂granules were dried at 120° C. for 2 hours, and calcined at 500° C. for2 hours. As a result of analyzing components existing at the crosssection of the obtained catalyst by SEM analysis and electron microprobeanalyzer, an existence of the porous layer made of WO₃ at surface of theTiO₂ granules was confirmed.

A relationship between the conversion rate of CFC 12 and the reactiontime is indicated in FIG. 9. The catalyst using titania granulesobtained by granulation as for raw material has relatively smallfluctuation in the conversion rate in accordance with relapsing time.Therefore, the titanium oxide granules obtained by granulation areadequate as for the raw material of the catalyst.

(Experiment 9)

In the present experiment, the activity of the catalyst which wasprepared using TiO₂ granules manufactured by granulation was againexamined. However, a method for granulation differs from the experiment8.

Concretely, granular titanium oxide (made by Sakai Chemical Co., CS-224)of 2˜3 mm in diameter was pulverized in an automatic mortar, and thepowder was dried at 120° C. for 2 hours. Then, the dried titanium oxidepowder 100 g was mixed sufficiently with ammonium paratungstate 41.1 gusing a kneader with adding distilled water. After drying the obtainedslurry at 150° C. for 2 hours, the obtained powder was calcined at 500°C. for 2 hours. Then, the obtained powder was loaded into a die andfabricated by pressing with a pressure of 500 kgf/cm². The fabricatedbody was crashed and sieved to obtain titanium oxide granules of 0.5˜1mm in diameter. Then, a hydrogen peroxide aqueous solution containingammonium paratungstate 41.1 g was impregnated into the obtained TiO₂granules 100 g. The catalyst was prepared by drying the TiO₂ granules at120° C. for 2 hours after the impregnation, and calcining at 500° C. for2 hours. As a result of analyzing components existing at the crosssection of the obtained catalyst by SEM analysis and electron microprobeanalyzer, an existence of the porous layer made of WO₃ at surface of theTiO₂ granules was confirmed.

A relationship between the conversion rate of CFC 12 and the reactiontime is indicated in FIG. 10. The titania granules obtained by the abovedescribed method for granulation are confirmed to be adequate as for rawmaterial of the catalyst.

(Experiment 10)

In the present experiment, the activity of the catalyst which wasprepared by mixing dried TiO₂ granules and ammonium paratungstate withadding hydrogen peroxide, instead of the method used in the aboveexperiment 9 wherein titanium oxide granules were impregnated withhydrogen peroxide aqueous solution dissolving ammonium paratungstate,was examined. By using hydrogen peroxide, tungsten can be dispersed morehomogeneously.

The conversion rate of CFC 12 by the present catalyst is indicated inFIG. 11.

(Experiment 11)

In the present experiment, the activity of the catalyst which wasprepared by an impregnation method other than the experiment 1 wasexamined.

The catalyst was prepared by impregnating a hydrogen peroxide aqueoussolution containing ammonium paratungstate 82.2 g into titanium oxidegranules 100 g, drying the titanium oxide granules at 120° C. for 2hours after the impregnation, and calcining at 500° C. for 2 hours. Theconversion rate of CFC 12 by the present catalyst was 99.9% at 50 hoursafter starting up of the reaction.

(Experiment 12)

In the present experiment, the activity of the catalyst which wasprepared from other tungsten raw material was examined.

The catalyst was prepared by impregnating a hydrogen peroxide aqueoussolution containing phosphotungstic acid 75.6 g into titanium oxidegranules 100 g used in the experiment 1, drying the titanium oxidegranules at 120° C. for 2 hours after the impregnation, and calcining at500° C. for 2 hours. The conversion rate of CFC 12 by the presentcatalyst was 99.9% at 50 hours after starting up of the reaction.

(Experiment 13)

In the present experiment, the activity of the catalyst which containssulfur was examined.

The catalyst was prepared by impregnating a hydrogen peroxide aqueoussolution containing paratungstate 82.2 g into titanium oxide granules100 g used in the experiment 1, drying the titanium oxide granules at120° C. for 2 hours after the impregnation, impregnating 0.1% sulfuricacid 75 g into the titanium oxide granules, drying again the titaniumoxide granules at 120° C. for 2 hours, and calcining at 500° C. for 2hours. The conversion rate of CFC 12 by the present catalyst was 99.9%at 50 hours after starting up of the reaction.

(Embodiment 3)

In the present embodiment, an apparatus for performing the treatingmethod for decomposing organohalogen compound relating to the presentinvention is explained referring to FIG. 12.

Organohalogen compound gas 1 (taken CFC 12 for an example in this case)recovered from wasted refrigerators, wasted automobiles, and the like,is determined its concentration by an analyzer 3 such as FIDgaschromatography, and is diluted with air 2 to adjust the CFC 12concentration to about 3% by volume. After adding water vapor 4 of 5times moles of the CFC 12 moles to the adjusted CFC 12 gas, the CFC 12gas is conducted to a reactor 20 having a catalyst layer 5 filled withthe catalyst relating to the present invention. The space velocity(space velocity=gas flow rate (ml/h)/volume of the catalyst (ml)) of thegas in this case is in a range of 5,000˜100,000/hour. The catalyst layer5 is heated by an electric furnace. As for a method for heating thecatalyst, a method conducting high temperature gas, which is obtained byburning propane gas and others, into the reactor can be used.Decomposition produced gas of the organohalogen compound is contactedwith sodium hydroxide aqueous solution sprayed from spray nozzles 7 andbubbled into alkaline absorbers 8. The gas passed through the alkalineabsorbers 8 is conducted into an adsorber 9 which is filled with activecarbon, and the like, and released to atmosphere. The liquid sprayedfrom the spray nozzles 7 can be only water, or slurry such as calciumcarbonate slurry. Wasted alkaline aqueous solution 10 in the alkalineabsorbers 8 is taken out regularly, and changed with new alkalinesolution 11. As for the alkaline solution to be sprayed from the spraynozzles, the alkaline solution in the alkaline absorber 8 is circulatedby a pump 12 and used.

(Embodiment 4)

In the present embodiment, an apparatus for performing the treatingmethod of the present invention is explained when the organohalogencompound is liquid at a room temperature referring to FIG. 13.

The apparatus is provided with further a preheater 14 to the decomposingapparatus for organohalogen compound in the embodiment 3. When theorganohalogen compound is liquid at a room temperature such as CFC 113liquid 13, the liquid is vaporized at the preheater 14. Then, itsconcentration is determined by an analyzer such as a FIDgaschromatography, and the concentration of CFC 113 is adjusted to about3% by volume by diluting with air. Subsequently, the CFC is treated bythe same manner as the embodiment 3.

In accordance with the present invention, organic compounds containingany of fluorine, chlorine, and bromine such as chlorofluorocarbons(CFCs), trichloroethylene, methyl bromide, halon, and the like, can bedecomposed with a high efficiency, and the activity of the catalyst canbe maintained for a long time.

What is claimed is:
 1. A method for treating organohalogen compounds, comprising a step of hydrolyzing the organohalogen compounds by contacting a gas flow containing the organohalogen compounds with a catalyst in the presence of water vapor at a temperature in a range of 200°˜500° C., whereinsaid catalyst comprises titania and tungsten oxide with an atomic ratio of Ti and W in a range from 20 mol % to 95 mol % Ti and from 5 mol % to 80 mol % W, and said gas flow contacts with said catalyst wherein a surface of the titania is covered with a porous layer of the tungsten oxide.
 2. A method for treating organohalogen compounds as claimed in claim 1, wherein said gas flow contains less than 30% by volume of said organohalogen compounds.
 3. A method for treating organohalogen compounds as claimed in claim 1, wherein said porous layer composed of the tungsten oxide has a thickness in a range from 1 Å to 5 mm.
 4. A method for treating organohalogen compounds as claimed in claim 1,wherein said catalyst is a catalyst prepared by a method comprising the steps of: impregnating TiO₂ granules with a solution containing W, and calcining the TiO₂ granules for converting W to WO₃.
 5. A method for treating organohalogen compounds as claimed in claim 1, wherein the catalyst consists essentially of titania and tungsten oxide.
 6. Catalyst for decomposing organohalogen compounds in a gas flow containing said organohalogen compounds by hydrolysis in the presence of water vapor, whereinsaid catalyst comprises titania and tungsten oxide, said catalyst has an atomic ration of Ti and W in a range from 20 mol % to 95 mol % Ti and from 5 mol % to 80 mol % W, and at least a surface of said titania is covered with porous layer of tungsten oxide.
 7. Catalyst for decomposing organohalogen compounds as claimed in claim 6, whereinsaid porous layer composed of the tungsten oxide has a thickness in a range from 1 Å to 5 mm.
 8. Catalyst for decomposing organohalogen compounds as claimed in claim 6, whereinwherein said catalyst is a catalyst prepared by a method comprising the steps of: impregnating TiO₂ granules with a solution containing W, and calcining the TiO₂ granules for converting W to WO₃.
 9. Catalyst for decomposing organohalogen compounds as claimed in claim 6, whereinthe titania is TiO₂ granules, and WO₃ is dispersed inside the TiO₂ granules.
 10. Catalyst for decomposing organohalogen compounds as claimed in claim 6, whereinthe titania is TiO₂ granules, and said TiO₂ granules are prepared by granulation.
 11. Catalyst for decomposing organohalogen compounds as claimed in claim 6, whereinsaid catalyst includes at least one of S, P, Mo, and V with a concentration in the range of 0.001˜30 mol % to Ti atoms, and said S is contained as sulfate, said P is contained as phosphate, and Mo and V are contained as oxides.
 12. Catalyst for decomposing organohalogen compounds as claimed in claim 6, whereinthe tungsten oxide is also dispersed in the interior of the titania.
 13. Catalyst for decomposing organohalogen compounds as claimed in claim 6, consisting essentially of titania and tungsten oxide.
 14. A method for preparing catalyst used for hydrolyzing organohalogen compounds, comprising the steps of;impregnating TiO₂ granules with a solution containing W into inside the TiO₂ granules so that said catalyst contains Ti and W with an atomic ratio of Ti and W in a range from 20 mol % to 95 mol % Ti and from 5 mol % to 80 mol % W, and calcining the TiO₂ granules for converting W to WO₃ so that surface of said titania is covered with porous layer of the tungsten oxide.
 15. A method for preparing catalyst used for hydrolyzing organohalogen compounds as claimed in claim 14, whereinsaid solution containing W is a hydrogen peroxide aqueous solution.
 16. A method for preparing catalyst used for hydrolyzing organohalogen compounds as claimed in claim 14, whereinthe surface of said titania is covered with the porous layer of the tungsten oxide so as to prevent poisoning of fluorine to the titania. 